The invention relates generally to hydraulic systems. More particularly, this invention relates to the delivery and control of fluid power to a service truck to operate equipment on or near the truck, for example, but not limited to, a crane with multiple functions.
Existing work vehicles often integrate auxiliary resources, such as electrical power, compressor air service, and/or hydraulic service, directly from the mechanical power of the main vehicle engine. Specifically, the main vehicle engine may drive a power take-off (PTO) shaft, which in turn drives the various integrated auxiliary resources. This is common in many applications where the auxiliary systems are provided as original equipment, either standard with the vehicle or as an option. The work vehicles also may include a clutch or other selective engagement mechanism to enable the selective engagement and disengagement of the integrated auxiliary resources.
Unfortunately, these integrated auxiliary resources rely on operation of the main vehicle engine. The main vehicle engine is typically a large engine, which is particularly noisy, significantly over powered for the integrated auxiliary resources, and fuel inefficient. For example, the main vehicle engine may be a spark ignition engine or a compression ignition engine (e.g., diesel engine) having six or more cylinders. The main vehicle engine may have over 200 horsepower, while the integrated auxiliary resources may only need about 20-40 horsepower. Unfortunately, an operator typically leaves the main vehicle engine idling for extended periods between actual use of the integrated auxiliary resources, simply to maintain the option of using the resources without troubling the operator to start and stop the main vehicle engine. Such operation reduces the overall life of the engine and drive train for vehicle transport needs.
Furthermore, the vehicle with integrated auxiliary resources does not control the power consumption, because the main vehicle engine has equal or more power than what is needed under all maximum power consumption circumstances (e.g., full hydraulic flow and pressure). Instead, the main vehicle engine typically runs at a normal condition without any change despite the various loads associated with the integrated auxiliary resources. At this normal condition, the main vehicle engine generally provides a great deal of wasted power.